Managing the water balance of The Fayoum Depression,Egypt

A study of the water balances of The Fayoum irrigated lands and Lake Qarun was made to investigate the management of the irrigation system and the efficiency of irrigation water use. The two water balances are strongly interrelated. The drainage flow to Lake Qarun and the water level of the Lake are in delicate balance. A rise in Lake level causes the inundation of adjacent land. Management of The Fayoum water balance assumes control over irrigation water flows, but this control has technical and organizational limitations. Also discussed is the influence of irrigation practices in The Fayoum on the water balance (e.g., the autumn flushing of fields and farmers' preference for not irrigating at night in winter). Notwithstanding a high overall efficiency, irrigation efficiency during the winter is low. The reasons for this are given, together with the constraints against improving system management. Improved uniformity of the division and application of irrigation water will enable a better technical control of flows and will result in better water management in The Fayoum. Abbreviations: FID — Fayoum Irrigation Department, 1 feddan (fe) — 0.4 ha, 1 mcm — 1 million cubic metres: an average annual flow of 3.17 m³/s gives 100 mcm, m³/fe.year — supplied volume (m³) per surface area (fe) per year: 1000 m³/fe.year equals 240 mm/year, MSL — Mean Sea Level     

Simulation of growth and production in sheep-model 1: A computer program to estimate energy and nitrogen utilisation,body composition and empty liveweight change,day by day for sheep of any age

A computer program based on empirical relationships is described. It predicts daily energy and nitrogen utilisation repetitively for sheep of any age, before, during and after weaning; provision is also made for pregnancy, lactation and cold stress. Input information includes: intake, protein content and digestibility of the diet; age, empty body weight, fat content and feeding activity of the sheep; ambient temperature and wind speed; times of shearing and mating.Metabolisable energy from milk and/or dry feed is estimated and energy requirements for maintenance, including the cost of feeding activities and homeostasis in the cold, are deducted to obtain energy balance. The amount of amino acid nitrogen absorbed from the small intestine is estimated, and nitrogen balance in body tissues and wool is calculated from this, allowing for body weight and net energy intake. Potential wool growth is calculated from nitrogen and energy intakes, and potential conceptus growth or milk production is estimated primarily from stage of pregnancy or lactation. The use of nitrogen and energy for these products is assessed and balances of energy and nitrogen in body tissues are then obtained by difference. If achievement of the potential rates of production in pregnant or lactating animals would cause excessive loss of energy or nitrogen from body tissues, production of wool and conceptus or milk is reduced sufficiently to avoid this problem. Gain or loss of body fat and protein, and hence change of empty live weight, are finally derived and the animal parameters are incremented before proceeding to calculation for the next day.Evidence is presented that the model is stable in predicting lifetime performance, and that predictions of growth curves, body composition and various nutritional parameters are reasonably accurate in a variety of circumstances.     

A review of irrigation performance assessment in California

A survey of irrigation performance assessment as conducted in California was performed. Emphasis was placed on the actual procedures employed by the State's major water providers and irrigation districts. Survey results covered the development of innovative irrigation performance assessment parameters as well as the methodologies used to evaluate these parameters. All aspects of California's irrigation infrastructure were considered, from the management of major hydraulic structures, through water delivery, and on-farm consideration. Environmental performance assessment methodologies were also examined.     

Division of irrigation water in The Fayoum,Egypt

The division of irrigation water in The Fayoum, Egypt, has been measured. Factors influencing this division are discussed: the hydraulic conditions at structures and canals, the operation regime of gates, lack of reliable gauge data for system operation, shortage of labour, and the water level in Lake Qarun. A deviation from uniform supply has been found for the entire Fayoum, but also along a lateral and sub-lateral. The reasons for this are discussed and suggestions for possible technical improvements of The Fayoum system are given.Abbreviations FWSBM Fayoum Water and Salt Balance Model Project - MSL Mean Sea Level at Alexandria - FID Fayoum Irrigation Department - mcm million cubic metres     

Farmers' irrigation practices in a high rainfall area

Recent droughts in the humid southeastern United States have focused attention on the need for and use of supplemental irrigation. Total annual rainfall amounts are sufficient for most crops in the region. However, erratic distribution of rainfall and the low water-holding capacities of most soils in the region cause frequent drought stresses in many crops. An on-farm study was conducted in southeastern Alabama to evaluate the effects of farmers' irrigation scheduling decisions on soil moisture variations in peanut fields irrigated with center-pivot irrigation systems. The study showed that the way irrigation was practiced in this high rainfall area often caused soil moisture deficit (SMD) level higher than the desired SMD limit during over 20% of the 140-day growing season. This is partially due to farmers' tendency to delay irrigation in anticipation of rainfall which may or may not occur, as rainfall during the growing season is often erratic and local. In contrast SMD in non-irrigated fields was higher than the SMD limit for half of the growing season.Abbreviations SMD soil moisture deficit - ET evapotranspiration - R_eff effective rainfall - WHC water holding capacity     

Water use estimates for various rice production systems in Mississippi and Arkansas

Rice irrigation-water use was estimated in Mississippi (MS) and Arkansas (AR) in 2003 and 2004. Irrigation inputs were compared on naturally sloping (i.e. contour-levee system) and mechanically graded fields. In MS, rice production consumed, on average, 895 mm water, but irrigation inputs were greatly affected by production system. Contour-levee systems accounted for 35% of the production area and consumed 1,034 mm irrigation. Fields mechanically graded to a consistent slope of approximately 0.1% (i.e. straight-levee systems) consumed 856 mm irrigation and accounted for 60% of the production area. Fields devoid of slope (i.e. zero-grade system) accounted for 5% of the production area and consumed 382 mm irrigation. In AR, contour-levee rice production consumed 789 mm compared to 653 mm with a straight-levee system. Using low pressure, thin wall (9–10 mil) disposable irrigation tubing to deliver water to each paddy independently reduced irrigation inputs by 28% in MS and 11% in AR when compared to a single-point (levee-gate) distribution system.     

The growth and nitrogen economy of rice under sprinkler and flood irrigation in South East Australia

Summary Dry-seeded rice (Oryza sativa L., cv. Calrose) was subjected to 4 irrigation treatments — continuous flood (CF) and sprinkler irrigation at frequencies of one (S1 W), two (S2W) and three (S3W) applications per week — commencing 37 d after 50% emergence (DAE). The amount of water applied was calculated to replace water lost by pan evaporation. Urea (120 kg N ha^–1) was applied in a 1:1 split 36 and 84 DAE, and there were also unfertilized controls for each irrigation treatment. Amounts of nitrate (NO ₃ ^– ) in the soil were very low throughout the growing season in all treatments, despite regular periods of draining which lasted for up to 7 d in SlW. In all irrigation treatments, the majority of the fertilizer nitrogen (N) was located in the top 20 mm of soil. After each application of fertilizer, levels of mineral N in CF declined rapidly, while levels in S3W and S1W remained high for 1–2 weeks longer. The poor growth of sprinkler-irrigated rice was not due to lower amounts of mineral N in the soil. The greater persistence of fertilizer N in the sprinkler-irrigated treatments was probably due to reduced root activity near the soil surface because of frequent periods of soil drying in between irrigations. Net mineralization of soil N in the unfertilized sprinkler-irrigated treatments was reduced by about half compared with CF.On average, the quantity of water applied (1.2–1.4 × EP) to the sprinkler-irrigated treatments appeared to be sufficient to meet the evapotranspiration demands of the crop, except possibly around flowering time. However, the plants may have suffered from moisture stress in between irrigations. Soil matric potential data at 100 mm suggested little water stress in the sprinkler-irrigated treatments during the vegetative stage, consistent with the similar tiller and panicle densities in all irrigation treatments. However, the crop was stunted and yellow and leaf rolling was observed in the sprinkler-irrigated treatments during this period. Soil matric potential data at 100 mm indicated considerable water stress in S1W beyond the commencement of anthesis, and in S2W during grain filling, consistent with the reduced floret fertility and grain weight in those treatments.     

Crop water requirements for rainfed and irrigated grain corn in China

A basic parametric crop water use model (WATER) that employes climatic and environmental data to calculate temporal and spatial water consumption for a variety of major corps was applied specifically for grain corn to the region of China and Korea to investigate the evapotranspiration (ET) demand on grain corn and the associated irrigation water applications necessary for optimal crop production. A network of 241 stations provided the seasonal climatic input. The climatic input consisted of data averaged over approximately a 20 year period. Among the results, highest ET under full irrigation (first harvest) occurred in the northwestern inland sections of China, whereas least ET was found for the southeast. Under rainfed conditions, the relationship became nearly inverse. In order to achieve optimum crop yields, about 1000 mm of irrigation water was needed in the northwest, contrasted with none required in the south and east of China. A sensitivity analysis was applied to determine the degree of error introduced by faulty or uncertain environmental input data.     

Salinity,water management and fertility interactions on yield and nitrogen fixation in snap-beans

Summary Salinity, a common environmental constraint in arid and semiarid regions, causes substantial reduction in yield and nitrogen fixation in sensitive edible seed legumes. Greenhouse experiments were designed to determine whether irrigation and fertilizer supplements could reduce the adverse effects of soluble salts on yield and nitrogen fixation in a sensitive seed legume. Snapbeans, Phaseolus vulgaris L. cv Early Gallatin, inoculated with Rhizobium phaseoli L., were given 3 levels of irrigation salinity, 3 frequencies of irrigation and 2 N levels, and 3 P levels, on a P-deficient Argixeroll. Yield components, percent plant N, and acetylene reduction were reduced significantly as salinity and the interval between water applications increased. Fertilizer application had no effect on any plant component. Two- and three-way interactions confirmed the strong effects of the individual variables of salinity and irrigation frequency. Increasing irrigation frequency increased yield at all of the water salinities studied. Application of N, P, K fertilizers helped maintain yields at low to moderate levels of soil salinity, but not at high salt levels. Snap-bean plants harvested at seed maturity, however, did not show a significantly substantial benefit of fertilizer for Rhizobium in the stressed rhizosphere.